The prior art in hand saws includes three basic designs. The first and most common design involves a saw with a rigid frame in which the blade is tensioned at the ends so as to secure it in place. This type of saw is the most common variety of hand saw used for domestic and industrial purposes. The drawback with the rigid frame saw is that the blade is always exposed and the saw is not collapsible. Consequently, rigid frame saws are ideal for domestic and industrial use where portability is not required.
The second hand saw design involves a hand saw frame which includes hinges and can be folded and compacted via the hinge mechanism. The hinged frame provides for a hand saw that can be somewhat compact and portable. U.S. Pat. Nos. 4,580,344 (issued to Jinghage et al.), 3,905,409 (issued to Bradley), and 3,954,127 (issued to Doxon) disclose hinged frame saws. The Jinghage and Bradley saws are foldable triangular saws and the Doxon saw is a foldable bow saw. The Jinghage, Bradley and Doxon designs suffer from the typical drawbacks associated with hinged frame saws. The disadvantages include:
(i) the saws are relatively wide, making them more cumbersome, because the parts of a hinged saw frame fold in on one another and so must accommodate the other parts of the saw; PA1 (ii) hinged saws are generally restricted to light duty saws, because they lack the sturdiness and rigidity required for a heavy duty sawing, particularly in the hinge region, which is under a great deal of stress; and PA1 (iii) the addition of the hinge increases the overall weight, reducing the saw's portability. PA1 (i) the saw blade requires washers, which are attached to the blade by rivets. Over time, the washers can become worn and break or bend; PA1 (ii) the thumb nuts could easily become lost on a hiking trip, rendering the saw useless; PA1 (iii) the Bilsback saw has poor vertical clearance between the saw blade and the cross member; and PA1 (iv) in the compact mode, the thumb nuts on either side of the compacted tube add to its overall length. PA1 (i) the large support bar is very long and heavy (even in the collapsed configuration) because it must contain all of the other saw elements consequently, the support bar extends below the saw blade limiting the use of the saw, particularly for making flush cuts; PA1 (ii) the clip used to maintain the saw in the collapsed configuration may become easily lost; and PA1 (iii) the support bars have flat ends which are not shaped to be received by the handles; consequently, the frame is not very rigid and the saw blade may experience considerable torque because of the twisting frame. PA1 (i) the thumb screw/butterfly nut assembly adds extra length to the collapsed state; PA1 (ii) the possibility for the thumbscrew/butterfly nut assembly to become lost; and PA1 (iii) the lack of strength in the relatively flat brace bar.
The third hand saw design involves frames that are assembled from separate or severable components and are collapsible so as to remain easily portable. Once again, these designs are principally used for buck saws or triangular saws.
U.S. Pat. Nos. 4,287,922 (issued to Nelson), 4,186,785 (issued to Bilsback)and Canadian Patent No. 889,673 (issued to Moss). concern collapsible buck saws made from separate or severable parts. For these patents, the saw design includes a collapsed state, wherein all of the buck saw parts fit into the interior of the hollow tubular frame members, making the collapsed assembly easily portable.
Nelson discloses a buck saw having a single tubular cross member, with two pairs of support bars hinged onto the saw blade and shaped so as to slide perpendicularly through openings in the cross member. The Nelson apparatus is tensioned only by a loop of twine, which secures the support bars. Although the twine tension mechanism is extremely lightweight, the tension achievable in the Nelson design, is severely limited. Furthermore, the support bars provided for by the Nelson saw are not comfortable hand grips. These disadvantages make the Nelson buck saw suitable for only the most light duty sawing.
Bilsback discloses a buck saw that also has two tubular support bars, which form the handles of the saw when constructed. The support bars each have slots at one end that receive the saw blade. A rod shaped tensioner and a tubular cross members provide the support and tension for the apparatus. The cross member, is pushed into an aperture in the middle of each of the support bars and is used to maintain the separation of the support bars. The tensioner is located at the end of the support bars opposite to the saw blade. The tensioner, in combination with two thumb nuts, is operative to pull the support bars together and to exert outward tension on the saw blade. The problems with Bilsback include:
The Moss saw uses a large support bar with a closed end that is longer than all of the other saw elements including the saw blade. In the collapsed configuration, all of the elements of the Moss saw are longitudinally inserted into the large support bar. A smaller support bar with a closed end is slidably inserted into the large support bar and fastened with a small clip. In the functional configuration, the saw includes a tensioner that goes through one of the support bars and hooks to the second support bar of the saw, and puts the necessary tension on the saw blade. The disadvantages with the Moss saw include:
U.S. Pat. Nos. 3,905,409 (issued to Bradley) and 4,637,141 (issued to Allen) disclose collapsible triangular saws. Once again, the saws are collapsible so that all of the saw parts for each saw fit into a singular tubular shape that is also used to form part of its frame.
The Bradley saw is partially collapsible and partially hinged. The saw blade is attached to a brace bar with a special hook, such that it can be positioned at an angle with respect to the brace bar when in the functional configuration. One end of a tubular handle adjoins the brace bar at the side opposite the saw blade and forms a perpendicular angle therewith. The bottom end of the tubular handle is coupled to the second end of the saw blade with a hinged thumb screw/butterfly nut assembly. In this manner, the saw blade, brace bar and tubular handle form a functional triangular saw. When in storage mode, the brace bar and the saw blade slide longitudinally into the tubular handle. The thumbscrew/butterfly nut assembly is then used to secure the pieces in place so that the saw may be easily transported. The problems with the Bradley design include:
The Allen saw consists of two tubular pieces of different diameter such that one fits longitudinally into the other when in storage configuration. Each of the two tubes contains a slot at one end which is operative to hold the saw blade when the saw in is a functional configuration. In the functional configuration, the non-slotted end of the thin tube abuts against the cylindrical side wall of the wider diameter tube at a substantially perpendicular orientation. The saw blade is held in the saw blade slots at the opposite ends of the two tubular pieces. A tensioning device comprising a screw with a hook on one end and a thumb nut is then used to exert tension on the saw blade. The hook of the tensioning screw fits into a hole on the cylindrical side wall of the thin tube and the shaft of the tensioning screw pushes through two holes in the cylindrical side walls of the wider tube, where it engages the thumb nut. In the compact configuration, the saw blade slides longitudinally into the thin tube, which, in turn, slides longitudinally into the wider tube. The hooked end of the tensioning device also slides into the tube assembly, leaving the shaft of the tensioning screw pushing through the circular end of the wide tube where it engages the thumb nut, and operates to hold the compact apparatus closed.
The problems with the Allen design are best illustrated with reference to the figures in that patent document. FIGS. 8 and 9 depict the tensioning screw 18 with its shaft having a straight piece 90 with threads 98 and a bent section 96 with a hook 94. In FIG. 1, the saw is shown in its functional configuration. The problem with the design is that, while exerting sufficient force in the horizontal direction (i.e. along the thin tube 50), the tensioning screw exerts relatively little force in the vertical direction (i.e. along the wide tube 12). The slotted end 68 of the thin tube 50 is susceptible to being vertically displaced during a sawing motion. Consequently, the saw is not sufficiently rigid for heavy duty sawing applications and may break or come apart, subjecting the user to unnecessary danger.
A second disadvantage of the Allen design is the extra length of the compacted configuration that is required to accommodate the thumb nut of the tensioning device.
A final disadvantage with the Allen design is that the thumb nut of the tensioning device may be easily lost, particularly in the wilderness, rendering the device useless
In view of the foregoing disadvantages inherent in the known types of collapsible hand saws as taught in the prior art, the present invention serves a number of objectives.
It is a primary object of the present invention to provide a lightweight and portable saw that is collapsible into a single tubular shape, but may be configured to function as a triangular saw or both a triangular saw and a buck saw. These alternative configuration modes permit the apparatus herein disclosed to be used for both triangular saw applications (i.e. when there is limited room or a stronger saw is needed and when clearance between the blade and the top support bar is not important) and buck saw applications, which require a substantial clearance between the blade and the top support bar.
A second object of the present invention is to provide a saw without unnecessary torque on the saw blade that could cause the saw blade to break and possibly put the user's safety in jeopardy.
Another object of the present invention is to provide for a lightweight portable saw that may be converted easily into an outdoor cooking utensil with the addition of some simple accessories.
Another object of the present invention is to provide an apparatus which is stable, as small as possible, has the fewest number of pieces, has no small parts which may be easily lost and is lightweight, so that it may be easily carried while hiking or working outdoors on a tool-belt or a backpack.
Another object of the present invention is to provide an apparatus which is easily assemblable and dissassemblable into any of its various configurations.